This invention relates to an intravenous fluid supply system. More particularly, this invention relates to a device for regulating the rate of fluid flow through an intravenous line into a patient. This invention also relates to an associated method for controlling the rate of intravenous feeding.
In hospitals, intravenous infusion rates are stipulated by doctors' prescriptions which are usually specified in terms of cubic centimeters per hour. Such a prescription is usually converted by a nurse or other hospital personnel into a number of drops of intravenous fluid per minute. The drops are measured by monitoring a so-called "drip chamber" wherein drops fall from an inlet through an air space into a reservoir of fluid at the bottom of the drip chamber. Fluid then flows out through an outlet port at the bottom of the reservoir into an intravenous line extending to a patient. Depending on the model of drip chamber, a uniform size drop is produced, enabling conversion of cubic centimeters per hour into drops per minute. The number of drops per minute is controlled by adjusting a roller valve downstream of the drip chamber.
It would be desirable to dispense with the units conversion and the time consuming flow regulation procedure by providing a valve with a simple setting in terms of cubic centimeters per hour.
An intravenous system is a pressure driven system wherein pressure from an elevated bag or reservoir is fed through a drip chamber, sometimes a check valve, a regulating clamp, various hose fittings, and finally a cannula or catheter at the patient. All of these elements provide pressure loss, and it is the balancing of all these via the pressure loss in the regulating valve against the pressure from the bag that regulates flow.
In designing a system which is accurate and responsive, it is important to note that two factors vary from infusion to infusion. One factor is orifice size of the catheter or cannula. A pediatric version, for example, is smaller than adult sizes. Another factor is venous back pressure which varies somewhat from patient to patient. Occasionally, even the initial pressure source can be a variable if the height varies at which the bag is suspended. Viscosity of the intravenous fluid may also be a variable. In addition, pressure affecting factors can change even during infusion. The pressure provided by the bag decreases slightly as the level falls. A patient's venous back pressure can vary. The condition of the infusion site can change, resulting in a pressure loss. For these reasons, infusion rate is routinely checked and adjusted periodically by a nurse during an infusion.